config: add option for maximal udp payload

refs #159
man: update knot.conf.5
Merge branch 'set_edns_payload' of /git/repositories/labs/knot
nameserver: fix UDP payload size

Maximal UDP payload size is 512 B (excluding UDP header)
RFC 1035 #4.2.1
libknot: remove correlation between EDNS0 max udp payload and TCP message size

refs #160
typo
Merge branch 'tcp_payload_fix' of /git/repositories/labs/knot
Add beNNtoh support for glibc < 2.9
Merge branch 'byteorder' of /git/repositories/labs/knot
zscanner: add check for unclosed multiline block
config: properly close included files

refs #162
Merge branch 'config-includes-fclose' of /git/repositories/labs/knot